Giant Water Bugs

I knew I wasn’t going to get the right photo to fit today’s Photography 101 theme, moments and motion, because I feel like all the photos I’ve taken that have significant moments associated with them have been utterly serendipitous. I had a perfectly mundane day of meetings and e mails today, not the kind of day where I thought I’d come across a “moment” as I like to think of them. So, I decided to choose an older photo that represented a good moment for me. For those of you who have been reading my blog for a while, you may remember my sharing another photo from this series a few years ago:

I spent a decade studying giant water bugs (and am still studying them, just not full-time anymore). I absolutely love the species depicted here, Lethocerus medius, and they aregiant, scary looking insects that lurk underwater. I spent several summers collecting and working with the eggs. They hatch late at night, however, and since I kept them in the lab rather than at home, I always missed the hatching.

I got this photo when I was visiting a lab in another city to do some research I couldn’t do at my university. I was in the lab something like 16 hours each day and was just getting ready to leave one night when I caught a movement out of the corner of my eye. The tops of the eggs had popped open and the heads of the little bugs inside were visible. I was unbelievably excited – I was going to get to see them hatch! I spent over an hour watching them, taking photos as they progressed. The bugs all hatched at one time, swaying back and forth in unison as they pulled themselves out of their eggshells. I took several videos of their movement, little synchronized rhythmic insectoid waves. I still watch them a couple of times a year and remember.

A short while after I took this photo, it was obvious the bugs were about to come completely free, so I picked up the stick they were attached to. The freshly hatched bugs spilled out into my hands, a hundred or more all at once, and I dashed across the room so they could fall into the pan of water I had waiting. For me, it was a magical moment, little bugs slipping into the water between my fingers, a moment full of movement and life and pure joy, one that to this day I am thankful I was able to bear witness to.

That’s the sort of moment I thought of when I saw the theme “moments and motion,” the sort of moment you don’t expect and instead fall into randomly. My day today was not the sort of day when magical, memorable moments fall into your lap. Those don’t come so often, but I’m always happy to have my camera with me when they do.

Like this:

That’s a Lethocerus uhleri nymph, a very large giant water bug common in North Carolina. This particular individual was only an inch long when I scooped it out of the pond at work, but it was still a baby. They get quite a bit larger before becoming adults! I like the way that they looked wholly menacing, even as young’ins. :)

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I work with giant water bug eggs and need to know the exact date they were laid, so I need to keep bugs in the lab. This means I need to keep my bugs alive! Giant water bugs can live well over a year, so you need to have space and time to care for them if you’re going to bother. That said, giant water bugs are incredibly easy to care for! Here’s what I do for the back brooders that I use for my research.

Step 1. Collect bugs in the field.

Me collecting in Florida Canyon

I have several places I like to collect giant water bugs. One sire is part of the University of Arizona, the field research station for the Santa Rita Experimental Range at Florida Canyon. (That’s pronounced flor-EEEEE-dah, by the way.) There’s a great little pool, pictured above, located just downstream of the parking area. All I have to do is take my trusty soup strainer down and scoop bugs out. Transporting bugs back to the lab is the most tricky part of caring for them in the lab. They’re aquatic insects, but they rely on surface air and they drown more easily than you’d expect. You have to be very careful about how much water they’re sloshing around in. Water bugs are also rather cannibalistic, so it’s best to keep them separated. I usually place 2-3 bugs in a plastic bag with some wet vegetation gathered from the stream, then fill the bag with air before I seal it. Then I pack a whole bunch of bags into a cooler. Seems to work pretty well as I rarely end up with dead bugs, even if I have to leave them in the bags for a day or two.

Step 2. Introduce bugs to their new home.

Keeping the bugs separate is important, so I use a system my advisor developed:

Water bug condo!

Plastic Rubbermaind boxes make great containers for back brooders! Inside the box pictured here are a couple of little plastic blocks (not visible) that hold a sheet of plastic pegboard off the bottom of the box. Bugs are placed in individual plastic drinking cups. There’s a 1/2 inch hole in the bottom of each cup and each contains a small rock or cement block to give the bugs something to hold onto. I fill the box so that the water in the cups is about an inch deep. I can keep 15 bugs in each box without having to worry about them eating each other, so I can keep quite a few bugs in minimal space. It’s a great system. Wish I could take credit for it, but it was in place before I arrived and it’s all my advisor’s doing.

Step 3. Feed bugs.

Belostoma micantulum eating a mealworm.

Feeding the bugs is important. They need to eat to live of course, but if they don’t get enough to eat, they don’t produce eggs and I can’t do my work. Giant water bugs are also predators, so you’ve got to feed them animals. So, I feed my bugs mealworms once a week. Mealworms don’t move around much so the water bugs sometimes have a hard time recognizing them as food. Using a pair of forceps, I dangle a mealworm in front of a water bug and shake it around a bit. Usually the bugs will grab it right away and slowly eat it over several hours.

Step 4. Change the water.

Changing the water eliminates any wastes the bugs produce. Using the pegboard setup makes cleaning the containers is a breeze! I just take the lid off, pull the sheet of pegboard out with all the cups sitting on top, and set it on the lid. All the water drains out of the cups as you lift the pegboard. Then I simply dump the water in the sink, refill with water that’s been sitting out for a few days to remove the chlorine, and put all the stuff/bugs back in! You can easily clean 15 bugs in less than a minute.

Step 5. Mate the bugs to get eggs!

Giant water bugs mating (Abedus herberti)

Mating back brooders is incredibly simple. I’ve talked about how they mate in a previous post, but I didn’t discuss how I set up their mating chambers. It’s so easy! All you need are a few plastic bowls with lids (drill some holes in the lids so the bugs can breathe!), one medium sized rock to go in each bowl, and enough dechlorinated water to fill the bowls about 2 inches. Then you just place two well-fed bugs (a male and a female that have not been mated for at least three weeks) into the container, snap the lid on, and leave them overnight! Most of the time you’ll come back the next morning to freshly laid eggs. Sometimes you don’t and have to futz about a bit to get them to lay, especially during the winter, but most of the time you just get a male and a female together and let them go at it.

And that’s it! Caring for water bugs. Easy as pie. Well, easier actually. Pie can be rather tricky to make.

Posting might be a little light next week! Got things to do and people to see that might interfere with blogging, but I’ll be back to my regular schedule soon. Have a great weekend everyone!

Last week I covered some of my research with giant water bugs and described how one species, Abedus herberti, breathes. Respiration in this species is a fairly simple matter of going to the surface to collect a bubble of air that the bugs carry with them underwater, then using that air store as a source of oxygen while submerged. By adding two simple behaviors, gaping and dynamic gaping, the bugs can dramatically increase the length of time they can remain submerged. If you observe these behaviors and know a little something about aquatic insect respiration, it seems clear that these behaviors have some respiratory function. However, that’s not good enough for science! You have to provide evidence that a behavior does what you say it does. So, today I’m going to finish the A. herberti respiration story. First I’ll share the condition in which the bugs exhibit gaping and dynamic gaping and I’ll finish up by sharing how I know that these are indeed respiratory behaviors.

When you observe A. herberti in ideal conditions in the field, you notice that they prefer to stay within a few inches of the surface, usually holding onto the rocks along the banks of streams. They simply climb up the rocks and stick their air straps out to collect air, then crawl back down. This way they remain out of sight of predators, but still have easy access to the surface. However, not all bugs are in this sort of ideal environment. Some bugs need to dive further into the water to find a suitable perch, and they fight against the air bubble they carry the whole way down. With these observations in mind, you could imagine that bugs that can reach the surface easily might never use gaping and dynamic gaping. Bugs in deeper water, however, might want to stay underwater as long as possible because surfacing is hard work. If gaping and dynamic gaping are respiratory behaviors, you might expect bugs in deeper water to exhibit them more often than bugs in shallow water.

Shallow treatment

To test this idea, I did an experiment where I placed bugs in observation tanks filled with water to three different depths. In the shallow treatment, the bugs could reach the surface easily without letting go of the substrate. In the mid-depth treatment, the surface was just out of reach of the bugs as they did their surfacing behavior and they were forced to float to the surface. The deep treatment tanks contained water deep enough that the bugs were well out of reach of the surface. I placed bugs in the tanks one at a time and observed the behaviors of several bugs in each depth before comparing the treatments.

I learned that bugs forced to release their hold on the bottom are much more likely to use gaping and dynamic gaping than bugs that can reach the surface without letting go. A few bugs in the shallow treatment gaped and one dynamically gaped, but the behaviors were rare. Nearly every bug in the deep water gaped and dynamically gaped though, as did most of the mid-depth bugs. Thus, bugs forced to float to the surface and then swim back to the bottom are more likely to express both gaping and dynamic gaping than bugs that can reach the surface easily. Most likely, gaping and dynamic gaping require less energy than surfacing, so they do these behaviors to cut down on the number of trips to the surface they must make in deep water.

Exposing the air store during the gaping behavior

Once I established that water depth played a role in gaping and dynamic gaping, I set out to collect evidence that these behaviors were respiratory behaviors. I did two tests. In the first, I divided several bugs into two groups. I taped the wings to the abdomen using waterproof tape in the first group, preventing them from dynamically gaping or gaping. In the second group, I added the same amount of tape, but cut the strips in half so that they could do both behaviors. I then tested both groups to see how long they could stay underwater by forcing them to stay submerged until they showed signs of stress. I measured the length of time the bugs remained underwater before becoming stressed and the time spent gaping and dynamically gaping. The next day, I did it all again, except I reversed the treatments.

Abedus herberti at the surface

With this experiment I learned that when denied access to the surface, nearly all bugs exhibited both gaping and dynamic gaping when free to do so. The bugs were also able to remain underwater over three times as long when they could perform gaping and dynamic gaping than when they could not. This suggested that there was a respiratory purpose to the behavior, that bugs were able to absorb oxygen into the air store from the water when exposed and extend the length of time they could remain submerged. That is, they were using the air store as a physical gill.

To strengthen the evidence for a respiratory role for the behaviors even more, I did one final experiment. I once again forced the bugs to remain submerged until they showed stress, but allowed all bugs to perform gaping and dynamic gaping freely. I then altered the oxygen content of the water by bubbling air (adds oxygen) or nitrogen (removes oxygen) through a tank for 15 minutes before adding a bug. I divided the bugs and put half in the oxygen treatment and half in the nitrogen treatment the first day one at a time, then reversed the treatments the following day. Then I compared the time submerged, gaping, and dynamically between treatments.

Abedus herberti gaping

The results were clear: bugs in high oxygen water can remain submerged 10 times longer than bugs in low oxygen water. Bugs that could freely gape and dynamically gape could only remain submerged a few minutes in the low oxygen, nitrogen treated water while bugs in the high oxygen, air treated water were able to remain submerged nearly an hour. Clearly, the air store is acting as a physical gill. Bugs in low oxygen water weren’t able to remain submerged longer than bugs that were prevented from gaping and dynamically gaping entirely. In both cases, the air store was unable to absorb oxygen from the water. Bugs in the high oxygen water, however, were able to remain underwater much longer, strong evidence that the air store does act as a physical gill and absorbs oxygen from the environment when it is exposed to water.

So, the giant water bug Abedus herberti depends on oxygen at the surface, but it can extend the length of time the air store provides oxygen underwater by using two simple behaviors: gaping and dynamic gaping. I think it’s amazing that two seemingly insignificant behaviors, these tiny little movements, are capable of doing so much for these bugs. This sort of thing is why I love being a biologist! Isn’t nature marvelous?

Literature Cited:

Goforth, C. L. and Smith, R. L. 2012. Subsurface behaviours facilitate respiration by a physical gill in an adult giant water bug, Abedus herberti. Animal Behaviour: doi:10.1016/j.anbehav.2011.12.02. (Published online only currently – will replace this with the print citation when the issue is released)

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It’s the start of a new week and you know what that means: Science Sunday! I thought I’d mix things up a little today by talking about some of my own research. The subject of today’s post is this bug, a bug that should be quite familiar to my long-time regular (awesome!) readers:

Giant water bug, Family Belostomatidae, Abedus herberti

This is Abedus herberti, a giant water bug in the family Belostomatidae within the order Hemiptera (true bugs). It’s a large, aquatic insect native to Arizona and northern Mexico that you’ll find in streams, often in the mountains. It’s an interesting bug for many reasons, but it is especially well-known because the male bugs care for the eggs until they hatch (see my post about giant water bug parents for more details!) and they are wickedly efficient predators. These traits make these bugs fascinating for entomologists like me, but they’re not what got me interested in giant water bugs originally. I got excited about giant water bugs because of this:

Abedus herberti at surface, collecting air

Respiration! I never thought I would ever work with either insect respiration or aquatic insects (except dragonflies), but this project opened up a whole new world of possibilities to me and completely changed the direction of my research. So, today I’m going to tell you about the project. It’s too long for one post, so this week I’ll give you an overview of the respiratory behaviors of Abedus herberti and next Sunday I’ll talk about the experiments I did to show that this is a respiratory behavior.

Giant water bugs are aquatic insects and, as such, have several adaptations that allow them to live in water. I’ve talked about aquatic insect respiration before, so I’m not going to go over the respiratory adaptations again here, but note that giant water bugs depend on air to breathe. Water bugs in the genus Lethocerus have a long respiratory tube (called a respiratory siphon) that they stick out of the water that works a lot like a human using a snorkel. They also have a small space under their wings that holds a small amount of air so they can breathe underwater for a short time. (Imagine using a SCUBA tank – same deal!) Abedus herberti does things a bit differently. First, the respiratory siphon has been reduced to short air straps:

Abedus herberti. Arrow points to the air straps.

Second, it has a much bigger space under the wings. That means it can carry more air with it underwater and can remain submerged a lot longer.

So how does Abedus herberti breathe? Let’s trace the behavior from the moment the bug sticks its air straps out of the water, fills the space under its wings with air, and dives into the water to settle near the bottom. The bug then follows one of three behavioral pathways. The simplest is this: the bug absorbs oxygen from the air bubble into the body. When it has used up most of the oxygen, it goes to the surface to replace the bubble. If the bug’s close enough to the surface, it simply raises its abdomen and sticks the air straps out. If it’s in deeper water, it stretches as far as it can to try to reach the surface without letting go by raising the abdomen up, releasing the hind and middle legs, and holding on with only the front claws. If that’s not enough, it will let go completely, float to the surface, and quickly replenish the air store before diving to the bottom again. You can see the behavior in this rather blurry video:

That’s one behavioral pattern. In the second pattern, the bugs add one more step: gaping. The bugs surface, dive, and sit at the bottom, using the oxygen in the air bubble as before. However, after about 5 minutes they expose the air bubble to the water. To do this, they lower the abdomen, creating a space between the abdomen and the wings:

The giant water bug Abedus herberti gaping, exposing its air store to the water. The silvery part is the air bubble.

Gaping is a tiny behavior, one very small movement, but it does so much for the bug. By exposing the air bubble to the water, the bug transforms the air bubble from a simple oxygen store into a physical gill capable of absorbing oxygen directly from the water, tripling the length of time it can remain underwater! The bugs may gape for 20 minutes, then close the gap before returning to the surface.

The third behavioral pattern adds one important step: dynamic gaping. This pattern starts with the bug surfacing, diving, sitting on the bottom, and gaping. After gaping for 5 or more minutes, the bug starts doing this:

They do this motion over and over and over for up to three hours. Gaping allows the air store to become a physical gill, but dynamic gaping makes the physical gill function as efficiently as possible by stirring the water around the bubble. This pushes oxygen-depleted water away from the bubble and draws in oxygenated water. The physical gill is much less efficient at absorbing oxygen from the water when the bug gapes, but does not dynamically gape. Dynamic gaping is thus a form of ventilation that allows the bugs to remain underwater ten times longer than they can without gaping or dynamically gaping! But even a dynamically gaping bug must eventually return to the surface (see my post on better breathing underwater to learn why), so it closes the gap between the abdomen and wings and surfaces.

The advantages of this behavior are clear: gaping allows the bugs to remain underwater 3 times longer and dynamic gaping ten times longer than they can when they do not expose the air store to the water. But why is it important to stay underwater? This is one reason:

Egrets and other wading birds like to eat water bugs!

Many things love eating large, protein filled insects, so staying hidden underwater as long as possible likely helps A. herberti avoid predators. However, the bugs carry a lot of air with them, which makes them very buoyant. If they let go of the bottom, they float immediately to the top. Diving is probably very hard too because they have to fight against their tendency to float to the surface. So, if the bugs benefit from remaining underwater, but it’s hard to stay underwater, then it’s a good idea to stay underwater as long as possible. Gaping and dynamic gaping to the rescue! These two simple, easy behaviors greatly extend the length of time the bugs can remain submerged, but the behaviors probably also require far less energy than diving from the surface. If so, then gaping and dynamic gaping help the bugs avoid predators, save energy by avoiding trips to the surface, and maximize the time the bugs can spend trying to capture food.

So that’s gaping and dynamic gaping! Next week, I’ll discuss how I know that these are actually respiratory behaviors. I hope you’ll check back for part two!

Literature Cited:

Goforth, C. L. and Smith, R. L. 2012. Subsurface behaviours facilitate respiration by a physical gill in an adult giant water bug, Abedus herberti. Animal Behaviour: doi:10.1016/j.anbehav.2011.12.02. (Published online only currently – will replace this with the print citation when the issue is released)

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In case anyone reading this doesn’t know already, a large part of the research I do deals with giant water bug eggs. I spend a huge amount of my time staring at eggs with an electron microscope, rearing eggs, doing experiments on eggs, grinding eggs up to do chemical analyses, counting eggs… Perhaps I spend a little too much time with eggs, though I’ll leave you all to decide that on your own. Giant water bugs have a lot of interesting features to recommend them (including some really beautiful structures on the egg-shell), but I think one feature in particular is especially worth mentioning. If you know much about eggs in general, such as bird eggs, reptile eggs, or other insect eggs, you probably know that most animals lay their eggs and the embryos develop within the confined space inside. This isn’t what happens with giant water bug eggs! Instead, they absorb water (a lot of water!) and puff up the eggshell from the inside so they get bigger over time. In fact, giant water bug eggs, as big as they are to begin with, nearly double in size between the time they are laid to the time the nymphs hatch and swim away. Their eggs GROW! Simply spectacular.

For today’s special Friday 5+1, I’m going to share a series of photos I took of the eggs of the giant water bug Lethocerus medius a few years ago that show how they grow as they develop. It may a little difficult to see if you don’t spend as much time around these things as I do, but compare the Day 1 eggs to Day 6 eggs and you should be able to see the change clearly. I’m also going to give you a bit of commentary so you know what to look for. Let’s start at the obvious place…

Day 1.Lethocerus medius eggs start off just shy of 3 mm long and about 6 mg, a substantial insect egg. This species is an emergent brooding giant water bug (see my post about giant water bug child care for more information), so it lays its eggs on vegetation out of water. As you can see, the eggs are very tightly packed so that most of each egg is touching the others with only a small part of the top free:

Day 2. On the second day, things look rather similar from the outside, though the eggs get a little taller and a little heavier:

Day 3. By day 3, the eggs have gained almost half a millimeter in height and 0.2 mm in width. The weight has gone up too, nearly 2 mg. You can start to see the eggs bulging at bit at the top:

Day 4. The eggs are growing more noticeably now, gaining another 0.5 mm and 2-3 mg overnight! You can see how the eggs start to crowd each other a bit. They’re fixed in place at the bottom, but they start to spread out at the top so that they can all fit:

Day 5. By day 5, the eggs have stopped growing up and begin to grow out a bit, adding 1/10th of a millimeter and another 2-3 mg in weight. The eggs are now over 4 mm tall and 2 mm wide and weigh nearly 13 mg! The eggs continue to spread apart at the top end as they increase in size so that you begin to see gaps between the eggs and can start to see the sides of the eggs as well as the tops:

Day 6. During their last day in the egg stage, the eggs have topped an enormous 5 mm (that’s HALF A CENTIMETER! Huge!) in height, nearly 2.3 mm in width near the top of the eggs, and reached 14+ mg! These are truly big eggs now, and have nearly doubled in height in 6 days. You can see nearly all the way down to the stick in some of the gaps between the eggs and the eggs themselves look like they’re ready to pop:

If they make it this far, you’ll usually see the following events the same night. Hatching:

… and then the newly hatched nymphs swim away, leaving behind only a stick and some empty shells:

And there you have it! A wonderful set of growing insect eggs! Lethocerus medius isn’t the only water bug that exhibits this amazing growth either. Other giant water bugs have shown similar patterns, including a mix of emergent brooders and back brooders. Growing eggs seem to be quite common, if not universal, within the family to which the giant water bugs belong, the Belostomatidae. Just one more way that giant water bugs are among the most amazing insects ever!